This invention relates generally to improvements in prosthetic devices used for reconstructing human joints, such as a knee joint, hip joint, etc. More particularly, this invention relates to an improved prosthetic component and related method for cemented attachment of the prosthetic component to a prepared patient bone, in a manner achieving a substantially optimum strength attachment interface.
Artificial or prosthetic joint mechanisms for implantation into animals, particularly humans, have been the subject of intensive research and development efforts for many years. Such prosthetic joint mechanisms have typically comprised one or more implant components formed from a relatively biostable material having selected structural properties and a unique shape to replace all or part of a selected anatomical joint, for example, a hip or knee joint. The implant components are installed by surgically accessing the joint and by resection of one or more bone surfaces to accommodate direct attachment thereto of the implant components. One common attachment method has utilized bone cement, such as a methyl methacrylate-based cement or the like used as grouting material to fill up the space between the resected bone surface and the prosthetic component. Alternative attachment methods have relied upon surface coatings of controlled porosity on the prosthetic component in a position to achieve post-operative bone and/or tissue ingrowth.
Although cemented attachment of the prosthetic component can be performed relatively quickly and easily, and does not require a post-operative period during which the strength of the attachment interface is increased (e.g., by bone ingrowth), certain problems and disadvantages exist with respect to cemented components. More specifically, in a typical procedure, bone cement is applied to an attachment surface formed on the prosthetic component, and this attachment surface is then pressed against the prepared patient bone to achieve cemented fixation. However, during such press-on placement, some of the bone cement is normally extruded laterally outwardly from the attachment interface and is lost. Moreover, the prosthetic component can be pressed onto the patient""s bone in a slightly cocked or tilted position, so that the thickness of the cement mantle is thicker in some areas and thinner in others. Such nonuniform cement mantle thickness can result in an attachment interface having less than optimum strength, thereby creating an undesired risk of post-operative separation of the prosthetic component from the patient bone.
There exists, therefore, a need for further improvements in prosthetic components of the type adapted for cemented attachment to a prepared patient bone, to provide a cement layer and mantle of controlled and substantially uniform thickness at the attachment interface. The present invention fulfills these needs and provides further related advantages.
In accordance with the invention, an improved prosthetic component and related placement method are provided for cemented attachment of the prosthetic component to a prepared patient bone, with a cement layer and mantle of controlled and substantially uniform thickness at the attachment interface. The prosthetic component of the present invention is adapted for use in various prosthetic joints, such as a knee joint or hip joint and the like.
The prosthetic component of the present invention includes an attachment surface of selected and typically grooved configuration with a size and shape for substantially mated fit with a resected patient bone. A plurality of spacer pegs having a selected height are desirably provided in the preferred form and protrude outwardly from the attachment surface. The attachment surface is bounded by a flow restrictor wall, which, when the spacer pegs are provided, has a selected height greater than the heights of the spacer pegs. In one preferred form, the flow restrictor defines an undercut inboard surface extending upwardly from the attachment surface.
An intruder tool is provided for engaging the resected patient bone to form a shallow recess having a size and shape for seated reception of the flow restrictor wall on the prosthetic component. In a preferred form, the intruder tool comprises a base plate with a projecting cutter rim thereon to engage the patient bone and form the shallow recess therein. The base plate and rim of the intruder tool define an open sided cavity which can be used for receiving a quantity of bone cement that can be pressed into porous cancellous bone during the step of forming the shallow recess.
The flow restrictor wall cooperates with the attachment surface of the prosthetic component to define an open-sided cavity for receiving an additional quantity of the bone cement. A leveler tool has a head shaped for mating press-in reception into the prosthetic component cavity to spread the bone cement in a uniform layer to a height at least slightly above the tops of the spacer pegs but below the rim of the flow restrictor wall, with excess bone cement escaping through vent ports formed in the leveler tool head.
The prosthetic component is then press-fitted onto the prepared patient bone, with the flow restrictor wall seated into the shallow recess. In this regard, the shallow recess is formed at an appropriate depth so that the flow restrictor wall when contacting the bottom of said recess functions to orient the attachment surface at a predetermined spacing from the prepared patient bone. This spacing is further regulated by inclusion of the spacer pegs which have a height to contact and seat upon the prepared patient bone when the flow restrictor wall is seated within the shallow recess. The bone cement contained within the prosthetic component cavity is thus confined by the restrictor wall against escape, for intrusion into the patient bone and further to form a substantially uniform thickness mantle in intimate surface-to-surface contact between the patient bone and the implant prosthesis. A strong, substantially optimum strength cemented attachment interface is thus achieved.
In accordance with an alternative preferred form of the invention, the prosthetic component and the intruder tool may be constructed for size adjustment to accommodate use with a range of patient bone sizes. In this form, the prosthetic component comprises a pair of component members respectively including a slidably interfitting key and keyway together with means for locking said component members with the key in a selected position of adjustment relative to the keyway. The two component members further include respective, generally U-shaped segments of the flow restrictor wall, with the ends of said U-shaped segments slidably overlapping within a range of size adjustment. The intruder tool also comprises a pair of tool members respectively including a slidably interfitting key and keyway with associated locking means, in combination with generally U-shaped cutter segments adapted to slidably overlap within a range of size adjustment to form the cutter rim.
Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.